1. Field of the Invention
The present invention relates to a vibration wave driven motor and, more particularly, to a vibration wave driven linear motor in which an elastic member, in which a travelling wave is formed, is pressed against a rail-shaped stator, and the elastic member is moved along the rail-shaped stator, and a printer utilizing the vibration wave driven linear motor.
2. Related Background Art
As a conventional vibration wave driven motor of this type, a motor shown in FIGS. 7 and 8 is known.
An elliptic elastic member 1 consists of a metal material having a projection 1a on its sliding surface side. A piezoelectric element 2 is joined to the upper surface of the elastic member 1 to form a vibration member. A travelling vibration wave is formed by applying an AC voltage to the piezoelectric element 2. A description of the generation principle of the travelling vibration wave and the structure of the piezoelectric element 2 will be omitted since they are known to those who are skilled in the art. When AC voltages having a 90.degree. temporal phase difference are applied to two driving piezoelectric element groups, which are positionally shifted by 90.degree., of the piezoelectric element, a travelling vibration wave is formed. A rail-shaped stator 8 is in frictional contact with the elastic member 1. The stator 8 is fixed to a bottom plate 10 of a motor case, and is maintained in contact with the elastic member 1 by a compression spring 3 via a vibration insulating material (e.g., felt) 5. A planar support plate 6 is fixed to the elastic member 1, and its central portion is fixed by a block-shaped support member 7, thus supporting the elastic member 1.
The elastic member 1 is supported by a base 4 via the support plate 6 and the support member 7, and the base 4 is supported by restricting members 9 each of which restricts displacements of the base 4 other than that in a prospective direction B.sub.Y.
When a travelling vibration wave is formed in the elastic member 1, the elastic member 1 moves along the rail-shaped stator 8 by a frictional force between the rail-shaped stator 8 and the elastic member 1, and the base 4 and other members 3, 5, 6, and 7 move in the direction B.sub.Y along the restricting members 9 upon movement of the elastic member 1. In this case, the generated frictional driving force acts on a portion of the elastic member 1, and this portion is shifted from the support portion. For this reason, a moment acts on the elastic member 1, and the elastic member 1 is liable to shift in the directions B.sub.X and B.sub.Y.
The support plate 6 has an X-shape, as shown in FIG. 9, and the four distal ends thereof are firmly joined to the inner side surface of the elastic member 1 by, e.g., spot welding. The central portion of the support plate 6 is firmly clamped by the support member 7, and the support member 7 is fixed to the base 4. For this reason, even when the moment acts on the elastic member 1, the elastic member 1 can smoothly linearly move together with the base 4 without rotating or cluttering.
Since this motor can perform position control in intermittent driving with high precision, it is proposed to use the motor as a motor for driving a print head in a known bubble-jet printer. A print head is mounted on a carriage (not shown) attached to the base 4, and the motor linearly reciprocally moves the print head.
However, in the above-mentioned prior art, since the rail-shaped stator 8 and the restricting members 9 comprise different members, and these members are elongated in the direction B.sub.Y, the rail and the restricting members considerably deform, and it is difficult to attain high flatnesses of the rail sliding surface, and the base of the restricting member.
Furthermore, since the bottom plate 10 to which the rail and the restricting member are attached consists of a thin plate, it is susceptible to a large deformation such as a warp. When the restricting members 9 and the rail-shaped stator 8 are attached to this bottom plate, the deformations of these members become worse.
For this reason, the parallel state of these guide surfaces, which guide the base 4, of the restricting members 9 at the two sides is impaired. Upon movement of the base 4 in the direction By, the inclination of the base 4 changes locally, and the gap between the rail sliding surface of the rail-shaped stator 8 and the base 4 undesirably changes.
On the other hand, the elastic member 1 is attached to the base 4 via the support plate 6 and the support member 7, and the compression spring 3 is also attached to the base 4. For this reason, when the gap between the rail sliding surface and the base 4 locally changes in the direction By, the compression force to be applied to the elastic member 1 varies, and a stable driving force of the motor cannot be obtained. When the inclination of the base 4 locally changes due to the influence of the guide surfaces of the restricting members 9, the vibration member inclines accordingly, and the contact state between the rail sliding surface and the vibration member is impaired, thus deteriorating motor performance.
Furthermore, since the restricting members 9 receive a compression counterforce of the vibration member via the support member 7 for supporting the vibration member, the load resistance received by the base 4 is large in a guide mechanism of a sliding bearing, as shown in FIG. 7, resulting in a decrease in motor output.
For these reasons, a print result by the print head mounted on the base tends to be unclear.